The present invention relates to methods for the formation of photographic color images in photographic silver halide color materials.
Existing commercial photographic silver halide color materials form dye images by the reaction of oxidised p-phenylenediamine color developers with a color coupler. The color developing solutions employed contain the color developing agent and used developer solutions need to be disposed of safely. Attempts have been made to incorporate p-phenylenediamine color developing agents into silver halide photographic materials but these have had little success largely due to the pronounced staining produced.
The use of sulphonhydrazides as color developers in aqueous color developer solutions which form an azo dye on coupling with a color coupler are described in U.S. Pat. No. 2,424,256, U.S. Pat. No. 4,481,268 and copending British Application No. 9125688.3.
A problem encountered with this system is that it is difficult to obtain the desired hue for the magenta image, for example 1-naphtholic couplers give a violet hue.
European Patent Specification 0 331 185 A describes a class of 3-pyridinol color couplers which form cyan dyes with conventional phenylenediamine color developing agents. There is no suggestion that they will couple with sulphonhydrazide color developers of any sort.
The present invention provides a process in which a class of couplers are used with sulphonhydrazide color developers to form image dyes of desirable magenta hue.
According to the present invention there is provided a method of forming a photographic color image which comprises imagewise exposing a photographic silver halide color material and processing it with an alkaline processing solution in the presence of a sulphonhydrazide color developing agent and a 3-pyridinol color coupler optionally containing in the 2-position a ballasting group of such size and configuration as to render the coupler non-diffusible in photographic materials thus forming a magenta dye image by reaction of the oxidised color developing agent and the color coupler.
xe2x80x9cThe present invention also provides a color photographic material comprising at least two color-forming units sensitive to different regions of the spectrum each comprising a silver halide emulsion layer wherein the material contains in at least one said silver halide emulsion layer, a ballasted sulphonhydrazide color developing agent and a 3-pyridinol photographic color coupler capable of forming a magenta dye upon coupling with the oxidized form of said developing agent, both incorporated therein in droplets of a high boiling solvent.xe2x80x9d
Advantages of the present invention include being able to photographically generate image dyes of desirable magenta hue without the use of p-phenylenediamine developers and allowing both the coupler and the color developer to be incorporated in the photographic material.
The present invention further provides a color photographic material comprising at least two color-forming units sensitive to different regions of the spectrum each comprising a silver halide emulsion layer characterised in that the material contains in or adjacent said layer, a ballasted photographic color coupler and a ballasted sulphonhydrazide color developing agent incorporated therein in droplets of a high boiling solvent and wherein the color coupler is a 3-pyridinol containing in the 2-position a ballasting group of such size and configuration as to render the coupler non-diffusible in photographic materials.
In a preferred embodiment the invention provides a color photographic material in which the material is a multicolor photographic material comprising a support bearing a yellow dye image-forming unit comprised of at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow azo dye-forming coupler, at least one magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler at least one cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler.
The pyridinol color coupler preferably has the formula: 
wherein
R is an electron-donating group,
R1 and R2 are each hydrogen or a substituent or together complete a carbocyclic or heterocyclic ring which may be substituted, and
wherein at least one of R, R1 and R2 contain a ballasting group of such size and configuration as to render the compound non-diffusible in photographic materials.
Examples of groups R are alkyl, alkoxy, alkylthio, hydroxy, xe2x80x94NHCONHR3, xe2x80x94NHCOOR3, amino, alkyamino or acylamino any of which may contain further substituents, of which specific examples are: methyl, trifluoromethyl, ethyl, t-butyl, octadecyl, benzyl, phenyl, ball-SO2NHxe2x80x94, ball-CONHxe2x80x94, ball-NHSO2xe2x80x94, ball-NHCOxe2x80x94, R3CONHxe2x80x94, R3NHxe2x80x94, R3SO2NHxe2x80x94, R3NHxe2x80x94 and xe2x80x94COO-alkyl wherein ball is a ballast group and R3 is an alkyl or aryl group which may be substituted.
Examples of groups that R1 and R2 may represent are halogen (eg Cl, Br, F, I), alkyl, aryl, alkylaryl, arylalkyl, heterocyclic, amido, sulphonamido, carbamoyl, sulphamoyl any of which may be substituted.
Examples of rings that R1 and R2 may complete are benzene, naphthalene, pyridine or thiophene.
All the substituents referred to above should, as the skilled man will readily recognise, compatible with the function of the compound.
The azo dye is formed as illustrated below: 
wherein R4xe2x80x94NHNHSO2R5 represents the sulphonhydrazide developing agent.
The sulphonhydrazide color developing agent may have the formula:
R4xe2x80x94NHNHxe2x80x94SO2xe2x80x94R5xe2x80x83xe2x80x83(2)
wherein
R4 is an aryl or heterocyclic group which may be substituted, and
R5 is an alkyl or aryl group, either of which may be substituted, and
wherein
R4 or R5 contains a ballasting group of such size and configuration as to render the compound non-diffusible.
A preferred group of developing agents of formula (2) are those in which R4 is a heterocyclic group. Examples of R4 are benzoxazole, benzthiazole, benzimidazole and naphthoxazole, naphthothiazole, naphthimidazole, quinoline and quinoxaline radicals, and preferably a 4-quinazolinyl group.
Examples of R5 include alkyl, aryl, alkylaryl, arylalkyl or heterocyclic any of which may be substituted.
The coupler and the color developer may be incorporated in the photographic silver halide material or the developer. If incorporated in the material, the compound should have a ballasting group of such size and configuration to render it non-diffusible in the photographic material or be in the form of a polymeric coupler.
The ballast group may be attached to couplers of formula (1) by forming part of R, R1 or R2. The ballast group in the sulponhydrazides of formula (2) may be attached by forming part of either R4 or R5.
As is conventional with color couplers, the coupler and the developing agent may be incorporated in the photographic material in droplets of high boiling coupler solvent. The high boiling solvent used to incorporate the coupler and/or color developer in the photographic material may be any solvent known as a coupler solvent (and used for incorporating couplers into photographic materials). Many such solvents are listed in Research Disclosure Item 308119, December 1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom. The coupler and color developer may be incorporated in the same or different droplets of coupler solvent.
The pyridinol couplers used in the present invention may be prepared as described in xe2x80x9cPyridine and its Derivativesxe2x80x9d, Supplement Parts 1 and 3 (1974), ed. R A Abramovitch, Wiley Interscience, New York.
Examples of 3-pyridinol couplers of formula (I) are listed in the following table:
The fastness of the image dyes may be increased by coating a tertiary or quaternary amine at 25-50% molar laydown of coupler. An exemplary compound has the formula: 
Many examples of suitable sulphonhydrazide color developers are listed in U.S. Pat. No. 5,284,739. Specific examples include the following: 
The present photographic materials, after imagewise exposure, may be processed by treatment in an alkaline solution. In such a process oxidised color developer forms in areas of silver halide development and the oxidised form of the developer couples with the coupler to form image dye.
In a preferred embodiment, the alkaline solution contains an electron transfer agent (ETA), for example a pyrazolidinone. A specific ETA that may be used is 4-hydroxymethyl-4-methyl-1-phenylpyrazolidin-3-one.